CCG 0957 is a phase-I study to determine the toxicity of B43-PAP when given concurrently with a standard four drug re-induction (Vincristine, Prednisone, L'Asparaginase, Daunomycin) in pediatric patients with acute lymphoblastic leukemia (ALL). B43-PAP is an immunotoxin (monoclonal antibody-toxin conjugate) which has been studied for the past 9 years by Dr. Fatih Uckun at the Children's Cancer Group Immunotoxin Resource Laboratory in Minneapolis. Single institution studies have been done at the University of Minnesota. B43 is the monoclonal antibody selected for the protocol because it is targeted toward the CD19 antigen, which displays specificity for pre-B lineage ALL - the most common type of leukemia in children.